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Researcher ORCID Identifier
Parris: 0000-0002-0999-7738; Zierer: 0009-0008-4031-5855; Woods: 0000-0001-8412-1149; Webb: 0009-0005-0508-9029
Abstract
From February 2023 through August 2024, Kentucky Geological Survey (KGS) scientists measured methane emissions on 119 orphaned oil and gas wells distributed among 26 counties in eastern, south-central, and western Kentucky. Early measurements were done in partnership with the Well Done Foundation using a Ventbuster flowmeter (n = 41), whereas later measurements (n = 78) were done by KGS scientists using a SEMTECH High-Flow 2 sampler or a static chamber designed and fabricated at the University of Kentucky. The measurements were done in support of the Kentucky Division of Oil and Gas plugging program funded by the Bipartisan Infrastructure Law’s State Orphaned Well Program (Initial Grant Program, IGP). In addition, KGS scientists conducted 244 screening and post-plugging measurements on 32 wells. Methane emissions measurements—termed ‘main protocol’—were conducted on oil (n = 82), gas (n = 32), and injection (n = 5) wells. The average methane emission rate for all wells is 30.7 g/hr; however, the data are right-skewed because a small number of wells (n = 9) account for 90% of emissions. Emissions from gas wells (66%) are more likely to exceed 1 g/hr as compared to oil wells (24%), and average emissions for gas wells (77.1 g/hr) are greater than oil (14.5 g/hr) or injection wells (4.1 g/hr), although the standard deviations overlap. The magnitude of methane emissions is not correlated with completion age (r = 0.07) or total depth (r = 0.11). It appears, however, that wells with complete or nearly complete infrastructure are more likely to be high methane emitters as compared to wells where all or part of the well is open to atmosphere. We believe the infrastructure acts to maintain at least a partial lid on the reservoir, thereby maintaining reservoir pressure to drive methane emissions. Maintenance of reservoir pressure also precludes intrusion of atmospheric gas into the reservoir. Using the measured methane emissions (i.e., statistical sample) to estimate emissions for wells plugged in the IGP was done using statistical bootstrapping. This procedure, which uses measured data to produce a probability distribution for the mean, is useful for defining confidence intervals for non-normally distributed data. The results provide lower and upper bounds of 11 and 55 g/hr for the 95% confidence interval for the average emission rate. Applied to wells in the IGP, this suggests a range of avoided methane emissions equal to 61.2 to 305.9 tonnes per year.
Publication Date
10-4-2024
Series
13
Report Number
58
Digital Object Identifier (DOI)
https://doi.org/10.13023/kgs.13.ct.58
Spatial Coverage
26 Kentucky Counties: Allen, Breathitt, Casey, Christian, Clinton, Daviess, Estill, Grayson, Green, Hancock, Hart, Henderson, Hopkins, Knox, Laurel, Lee, Magoffin, McLean, Menifee, Powell, Rockcastle, Union, Warren, Wayne, Webster, Whitley
Temporal Coverage
Measurement Dates: 02.13.2023- 08.28.2024
Funding Information
Work in this report was funded by the Commonwealth of Kentucky (Division of Oil and Gas) through a grant provided to the University of Kentucky Research Foundation (#3200005275).
Archival?
Archival
Language
English
Repository Citation
Parris, T.M., Zierer, D.W., Woods, S.L., and Webb, S.E., 2024, Estimating Methane Emissions from Orphaned Oil and Gas Wells in Kentucky: Results from the Initial Grant Program: Kentucky Geological Survey, ser. 13, Contract Report 58, 41 p.
Gas Chemistry Source Summary
Methodology
A. Methane Measurements
i. Screening measurements: evaluated wells for main protocol measurements by documenting the well head infrastructure and where gas was seen, heard, or smelled coming from the infrastructure. Point-in-time concentrations of methane and other gases (H2S, CO, and O2) and lower explosive limit (LEL) concentrations were measured [FSA1] with a Honeywell GasAlertQuattro (percent level detection threshold).
ii. Main protocol measurements: used three methods to measure the methane emissions from orphaned wells.
a. Ventbuster Flow Meter: deployed a high sensitivity flow meter () over a leaking orphaned well using a chamber or attaching the flow meter to the leak point on the well. The flow meter recorded the rate of total gas flow over the test period of hours to days. The amount of methane emitted (g/hr) was estimated by measuring the concentration of methane using gas chromatography on a sample collected at the end of the test. Flow meter tests were done as part of a subcontract to the Well Done Foundation. Gas chromatography measurements were done at Critical Control Energy Services.
b. Static Chamber: for orphaned wells having a small surface footprint and leaking small amounts of methane (< 1g/hr), measurements were made by deploying a static chamber over the well head and measuring the change in methane concentration over time. The change in methane concentration was measured with a LICOR LI-7810 (0.6 ppb sensitivity for CH4).
c. SEMTECH Hi-Flow 2 Sampler: used to measure methane emissions without a need for a chamber or connection to the wellhead. The instrument includes a variable speed intake fan that flows gas through a pitot-based flow meter. The concentration of methane in the flow stream is measured with tunable diode laser absorption spectrometer. The intake fan and spectrometer are run with a battery-powered control and measurement module.
iii. Post-Plugging Measurements: Following plugging, screening and soil gas flux measurements were conducted on 32 wells that were previously emitting methane. A properly plugged well should, in theory, not emit methane or leak oil. Thus, each former well site was evaluated for anomalous gas emissions from the soil, oil staining on the ground, or unusual subsidence. Once the most likely position of the well was determined, we conducted a soil gas survey using the LI-7810 [FSA2.1]trace gas analyzer connected to the LI-COR Smart Chamber. Fluxes of methane and carbon dioxide between the soil and atmosphere were measured at five locations on the former well pad. The five measurements include positions of our best estimate of the former wellhead location and locations 1 m north, south, east, and west of the wellhead location. At each of these locations, the Smart Chamber was coupled to the ground surface with 8-inch collars. Two to three flux measurements were performed and averaged at each of the five locations.
iv. Gas Chemistry: For most main protocol measurements, gas samples were collected for further gas chromatography measurements to quantify concentrations of alkanes (methane through pentane or hexane) and N2, O2, CO2, and H2S. Gases were collected with an approximately 24-inch length of ¼-inch PTFE tubing attached to a bulb pump on the inlet side, with another length of tubing on the outlet side connected to a 1-liter Tedlar gas bag. Gas samples collected by the Well Done Foundation were analyzed at the laboratories of Critical Control Energy Services. Gas samples collected by KGS personnel were analyzed at KGS with an SRI 8610C gas chromatograph (GC).
B. Geospatial Hazard Potential Evaluation: Create a map of orphaned wells that represent the most potential environmental hazard (), we looked at various environmental and societal risks related to abandoned wells. An overall (cumulative) hazard score was calculated for orphaned oil and gas wells with known latitude and longitude (N = 14,710) as collected from the Kentucky Division of Oil and Gas website. The overall hazard score is the sum of the four major hazard categories: atmospheric hazard, decay hazard, environmental hazard, and public safety hazard. In summary, the atmospheric hazard score was based on potential methane emissions that might come from an orphaned well. The emissions potential is based on 119 methane emissions measurements taken by KGS scientists in 2023 and 2024 as part of the Initial Grant Program. The decay hazard score addresses potential degradation of wellhead infrastructure that might lead to environmental contamination. Potential degradation was based on the factors brine salinity in which geologically older reservoirs tend to have more saline brines, and the completion date of the well (age of the well). Older wells have had longer to degrade and therefore have higher potential environmental hazard as compared to younger wells. The environmental hazard score was based on the sum of the values for groundwater hazard (vertical distance between well total depth and estimated deepest occurrence of potable water), surface water hazard (based on proximity to the nearest water body or spring), inundation hazard (based on flood frequency data from the Natural Resources Conservation Service’s SSURGO database), and conservation hazard (based on location in U.S. Fish and Wildlife Service critical habitat). The public safety/wellness hazard was based on the sum of the values for drinking water hazard (based on an orphaned well’s proximity to a drinking water well), recreation hazard (based on location in a park, forest, or wildlife management area), population hazard (based on population density[FSA3.1] within a census tract), and environmental justice hazard (based on location in communities identified as disadvantaged by the Justice40 Initiative).